IPB

Welcome Guest ( Log In | Register )

7 Pages V  « < 3 4 5 6 7 >  
Reply to this topicStart new topic
Exoplanet Discoveries, discussion of the latest finds
nprev
post Feb 22 2017, 01:50 AM
Post #61


Senior Member
****

Group: Admin
Posts: 7989
Joined: 8-December 05
From: Los Angeles
Member No.: 602



Reminder to all: We do not discuss embargoed information here; always wait until the official release. Thanks! smile.gif


--------------------
A few will take this knowledge and use this power of a dream realized as a force for change, an impetus for further discovery to make less ancient dreams real.
Go to the top of the page
 
+Quote Post
hendric
post Feb 22 2017, 06:16 PM
Post #62


Director of Galilean Photography
***

Group: Members
Posts: 834
Joined: 15-July 04
From: Austin, TX
Member No.: 93



https://www.nasa.gov/press-release/nasa-tel...-planets-around

https://exoplanets.nasa.gov/trappist1/


--------------------
Space Enthusiast Richard Hendricks
--
"The engineers, as usual, made a tremendous fuss. Again as usual, they did the job in half the time they had dismissed as being absolutely impossible." --Rescue Party, Arthur C Clarke
Mother Nature is the final inspector of all quality.
Go to the top of the page
 
+Quote Post
HSchirmer
post Feb 22 2017, 06:57 PM
Post #63


Member
***

Group: Members
Posts: 278
Joined: 24-July 15
Member No.: 7619



QUOTE (hendric @ Feb 22 2017, 06:16 PM) *


http://www.trappist.one/
Go to the top of the page
 
+Quote Post
JRehling
post Feb 22 2017, 08:06 PM
Post #64


Senior Member
****

Group: Members
Posts: 1991
Joined: 20-April 05
Member No.: 321



This is quite an interesting and – IMO – surprising discovery for the sheer number of planets packed so tightly together. Six of the planets have orbital periods between 1.51 and 12.35 days. Not surprisingly, there are small-integer ratios galore between orbital periods. In terms of the shortest period, the next four are 8:5, 8:3, 4:1, and 6:1.

In terms of bolometric luminosity, the second, third, and fourth ones get about the same thermal input as Venus, Earth, and Mars. There's no doubt that whatever one considers to be earthlike context in terms of that alone, at least one of these planets has it.

And here's one of the interesting consequences: There are about 500 red dwarfs closer than this system. The probability of a transit for a single planet in the "habitable zone" of such stars is about 2.5%, which would mean 12.5 such systems. But if there are multiple planets per system, then the number of planets we can see transiting will be higher than ~12.5, perhaps double that. And that'll increase the bounty when the time comes that we can do serious follow-up science by examining spectra.

A decade or so from now, we may have spectra for something like 20-50 sub-Neptune-sized planets in the HZ of red dwarfs. That's a nice future set of results to look forward to.
Go to the top of the page
 
+Quote Post
ngunn
post Feb 22 2017, 09:03 PM
Post #65


Senior Member
****

Group: Members
Posts: 3434
Joined: 4-November 05
From: North Wales
Member No.: 542



QUOTE (JRehling @ Feb 22 2017, 08:06 PM) *
Not surprisingly, there are small-integer ratios galore between orbital periods.


And, if the Jovian system is anything to go by, these resonances will be evolving over time with each planet experiencing different episodes of orbital forcing, eccentricity change and tidal heating. So once the orbital/thermal history of the Galilean moons has been definitively settled the dynamicists will then have this diabolically complex and even more crowded planetary system to chew over.

Another curiosity is that the system lies within one degree of our ecliptic plane. Does this mean that seen from there our Sun would also exhibit planetary transits?
Go to the top of the page
 
+Quote Post
JRehling
post Feb 22 2017, 09:36 PM
Post #66


Senior Member
****

Group: Members
Posts: 1991
Joined: 20-April 05
Member No.: 321



QUOTE (ngunn @ Feb 22 2017, 02:03 PM) *
Another curiosity is that the system lies within one degree of our ecliptic plane. Does this mean that seen from there our Sun would also exhibit planetary transits?


Maybe. The ecliptic is the plane of Earth's orbit, and 1° would put the Earth almost 4 Sun radii above/below the Sun's disk as seen from afar. But the other planets are all separate players, so perhaps some of them happen to transit as seen from Trappist 1. The farther out you go, the less likely. Also note that close-in planets tend to orbit close to the star's plane of rotation, whereas planets further out tend to orbit in planes that are closer to one another than to the star's rotation. These are the things we've learned from other planetary systems. So if I had to bet, I'd bet that none of the solar system's planets transit as seen from Trappist 1. (A couple of pages of trigonometry could provide the answer.)

Roughly speaking, the probability of a planet orbiting a sunlike star at 1.0 AU transiting its star is 0.5%. Red dwarfs are smaller than the Sun but their, e.g., "habitable zone" is much closer in by an even larger factor, so planets orbiting red dwarfs and getting the same radiation as Earth have about a 2.5% probability of transiting. This – along with the intrinsic number of different types of stars – is why, when we get instruments that can detect the spectra of transiting HZ terrestrial planets, we should get a bonanza of red dwarf candidates vs. far fewer that orbit sunlike stars.

As seen from another system, the two most easily detectible planets in our solar system are Jupiter and Venus. Venus, because it is relatively large and relatively likely to transit the Sun; Jupiter, because its gravity would tug the Sun significantly for the Doppler method. Earth and Saturn are the next runners-up. Detecting Mercury would require the Sun to exhibit very low noise. Mars is a distant sixth. We have yet to have any methods that have much chance of detecting Uranus/Neptune analogs, though with microlensing, it's a longshot.
Go to the top of the page
 
+Quote Post
ngunn
post Feb 22 2017, 10:52 PM
Post #67


Senior Member
****

Group: Members
Posts: 3434
Joined: 4-November 05
From: North Wales
Member No.: 542



QUOTE (JRehling @ Feb 22 2017, 09:36 PM) *
the two most easily detectible planets in our solar system are Jupiter and Venus. Venus, because it is relatively large and relatively likely to transit the Sun; Jupiter, because its gravity would tug the Sun significantly for the Doppler method.


So in Trappist-1 we have detected the 'Venuses', but its 'Jupiters', if any, presumably would not transit but await discovery by longer term observation of the system for slow wobbles.
Go to the top of the page
 
+Quote Post
JRehling
post Feb 23 2017, 05:41 AM
Post #68


Senior Member
****

Group: Members
Posts: 1991
Joined: 20-April 05
Member No.: 321



QUOTE (ngunn @ Feb 22 2017, 03:52 PM) *
So in Trappist-1 we have detected the 'Venuses', but its 'Jupiters', if any, presumably would not transit but await discovery by longer term observation of the system for slow wobbles.


We don't know a lot about the outer systems of red dwarfs. In a case like this, the outer system may be empty, may have more terrestrial planets, or may have some bigger planets. Generally, red dwarfs have far fewer big planets than do solar-type stars, so it's quite plausible that there simply aren't any Jupiters.

There are many unknowns in exoplanet frequency concerning the norms of system architecture. We know quite well what the inner systems look like in terms of planet frequency by type (size and orbital period), but we don't have a lot of firm evidence about the dependencies, i.e.., if there is a planet of type X, how likely is it that the system also has a planet of type Y? In fact, I think it's rather challenging even to describe systematically these sorts of dependencies. It's troublingly verbose even if we use bins and talk about systems with multiple planets (e.g., if we have a Super Earth orbiting between 30 and 45 days and a Neptune orbiting between 60 and 90 days, then what is the probability of each size of planet with a period between 120 and 240 days?). But, because any such bins are arbitrary, I think the whole topic seems almost maddeningly complex.
Go to the top of the page
 
+Quote Post
nprev
post Feb 23 2017, 05:54 AM
Post #69


Senior Member
****

Group: Admin
Posts: 7989
Joined: 8-December 05
From: Los Angeles
Member No.: 602



ADMIN NOTE: All TRAPPIST-1 posts have been moved here from "Exoplanet Atmospheres." Please carry on; thanks! smile.gif


--------------------
A few will take this knowledge and use this power of a dream realized as a force for change, an impetus for further discovery to make less ancient dreams real.
Go to the top of the page
 
+Quote Post
TheAnt
post Feb 23 2017, 12:41 PM
Post #70


Member
***

Group: Members
Posts: 484
Joined: 12-February 12
Member No.: 6336



QUOTE (JRehling @ Feb 23 2017, 06:41 AM) *
..... I think the whole topic seems almost maddeningly complex.


It is complex indeed!
3 planets in the habitable zone, but will any of them turn out to be even close to that considering other conditions that just temperature?
It looks from the summary of this paper that they have tried to figure out if the planets might be habitable at all considering the very strong X-ray flux as they are quite close to the their primary star.

Press release from the horse's mouth, ESO Ultracool Dwarf and the Seven Planets.



Go to the top of the page
 
+Quote Post
hendric
post Feb 23 2017, 05:24 PM
Post #71


Director of Galilean Photography
***

Group: Members
Posts: 834
Joined: 15-July 04
From: Austin, TX
Member No.: 93



QUOTE (JRehling @ Feb 22 2017, 11:41 PM) *
But, because any such bins are arbitrary, I think the whole topic seems almost maddeningly complex.


Yeah, we have to be very very careful when we do datamining for correlations. I'm reading Standard Deviations by Gary Smith, and that's one of the big dangers to look out for when attempting to discuss data with many possible combinations. Even random data will have a few correlations if it's sliced and diced enough different ways. Experimental physics gets around this issue by doing calculations and flow development on a small subset of the data, and once a signal is detected, rerunning the analysis across the whole dataset.

ObXKCD: https://xkcd.com/882/


--------------------
Space Enthusiast Richard Hendricks
--
"The engineers, as usual, made a tremendous fuss. Again as usual, they did the job in half the time they had dismissed as being absolutely impossible." --Rescue Party, Arthur C Clarke
Mother Nature is the final inspector of all quality.
Go to the top of the page
 
+Quote Post
JRehling
post Feb 23 2017, 06:15 PM
Post #72


Senior Member
****

Group: Members
Posts: 1991
Joined: 20-April 05
Member No.: 321



The big reason why it is much easier to determine planet frequency for a given bin (size, period) than to determine the norms of system architecture is that the norms of orbital inclinations are unknown (and sure to vary from case to case).

When we search a star for 1 transiting planet, we know that the orientation of the putative planet's orbit to our line of sight is a random variable, and we can thereby take the number of detections and compensate for that random variable, which is very neatly described in terms of simple geometry.

But when we try to determine the frequency of pairs (of whatever types), the neatness falls apart and we have chaos, simply because we don't know what the probability is of a second planet transiting given that a first planet did. Clearly, these are not independent variables, but the degree of dependence is unknown. Compensating for the geometric variations is highly sensitive to what the norms are: If we knew that an inner planet's orbital inclination vs. the outer planet has a standard deviation of, say, 1°, then we would know precisely how much to compensate for the geometric factors and convert our observations into frequency measures. But if it's actually 1.5°, then our estimate is off by 50%. And to make this wildly complex, the relationship is sure to be a very complex function of the sizes of the planets, not only because of the dynamics of how their orbits evolved, but in how the system evolved during accretion.

It's possible to resolve this, eventually, by measuring the orbital inclinations between pairs, which can be done by measuring the duration of transits, but this requires a lot of data, because in any particular instance, two planets could both transit their star even if their orbits are highly inclined because the line where their planes cross could happen to go right through the star.

Even then, different stellar populations may be different in this regard, and large surveys will probably be biased in uncontrollable ways. For example, Kepler looked off the galactic plane, which ends up being a significant bias because metallicity varies with galactic latitude, and the formation of large planets correlates with metallicity!

Possibly the killer technology to end all of this horrible ambiguity will be when we can visually resolve planets orbiting solar-type stars at >0.5 AU. Then we will simply see whole systems and definitive data on orbital inclination dependence will come in in a rush.
Go to the top of the page
 
+Quote Post
fredk
post Feb 23 2017, 07:23 PM
Post #73


Senior Member
****

Group: Members
Posts: 3777
Joined: 17-January 05
Member No.: 152



QUOTE (JRehling @ Feb 22 2017, 10:36 PM) *
1° would put the Earth almost 4 Sun radii above/below the Sun's disk as seen from afar.

I find an ecliptic latitude of close to 38' for this star. For earth transits to be visible from the star, it'd have to be within about 1/4 deg of the ecliptic. So earth transits are definitely out.
Go to the top of the page
 
+Quote Post
ngunn
post Feb 23 2017, 07:38 PM
Post #74


Senior Member
****

Group: Members
Posts: 3434
Joined: 4-November 05
From: North Wales
Member No.: 542



When will we know we have fathomed the'norms of system architecture'? I'd say: when nature is no longer able to surprise us.

Not so very long ago people were willing to make general statements to the effect that other planetary systems, if they existed at all, would probably be much like our own. It seems to me the main thing we've learned since then is just how far we are from knowing the full scope of possibilities. It's not only hard parameters like system geometry, instrumental limitations and the like which cause biased data sets. There's a human contribution too because premature generalisation can all too easily limit what one chooses to go looking for. Now that one is going to be really hard to quantify.

EDIT - Fred I was going from this map when I estimated 1 degree: http://www.trappist.one/images/aquarius_T1_thin.jpg
Go to the top of the page
 
+Quote Post
hendric
post Feb 23 2017, 08:27 PM
Post #75


Director of Galilean Photography
***

Group: Members
Posts: 834
Joined: 15-July 04
From: Austin, TX
Member No.: 93



If I am reading the Simbad entry correct for Trappist 1

http://simbad.u-strasbg.fr/simbad/sim-id?I...3062928-0502285

then it has a high proper motion with a -471 mas change in declination per year. I am handwaving the difference between the ecliptic and the celestial equator because I can. smile.gif

Given fredk's numbers of 38-15 = 23 arc minutes away from ecliptic, or 1380 arc seconds.

1380/.471 ~= 3000 years

So TRAPPIST-1 will be able to observe Earth transits a few thousand years from now.

The rest of the planets are inclined > 3/4* to the ecliptic, so unless they just happened to cross near TRAPPIST-1, they won't cause transits.


--------------------
Space Enthusiast Richard Hendricks
--
"The engineers, as usual, made a tremendous fuss. Again as usual, they did the job in half the time they had dismissed as being absolutely impossible." --Rescue Party, Arthur C Clarke
Mother Nature is the final inspector of all quality.
Go to the top of the page
 
+Quote Post

7 Pages V  « < 3 4 5 6 7 >
Reply to this topicStart new topic

 



RSS Lo-Fi Version Time is now: 20th October 2017 - 11:15 PM
RULES AND GUIDELINES
Please read the Forum Rules and Guidelines before posting.

IMAGE COPYRIGHT
Images posted on UnmannedSpaceflight.com may be copyrighted. Do not reproduce without permission. Read here for further information on space images and copyright.

OPINIONS AND MODERATION
Opinions expressed on UnmannedSpaceflight.com are those of the individual posters and do not necessarily reflect the opinions of UnmannedSpaceflight.com or The Planetary Society. The all-volunteer UnmannedSpaceflight.com moderation team is wholly independent of The Planetary Society. The Planetary Society has no influence over decisions made by the UnmannedSpaceflight.com moderators.
SUPPORT THE FORUM
Unmannedspaceflight.com is a project of the Planetary Society and is funded by donations from visitors and members. Help keep this forum up and running by contributing here.